1. Field of the Invention
The present invention relates to a modified nucleotide molecule of xylanase and use thereof, especially to a method for producing xylanase using the nucleotide molecule.
2. Descriptions of the Related Art
Xylanase is a main enzyme decomposing hemicelluloses among carbohydrate hydrolysis enzymes. Xylanase can be widely used, e.g., in food, in animal feed compositions, in textile or in papermaking applications, etc. For example, xylanase can be used to treat feeds for poultry to promote the break-down of anti-nutritional factors in feeds, which leads to better utilization of the nutrients and improving the growth of poultry. In addition, when added to dough, xylanase improves the mechanical strength of the dough, thereby, improving the lightness and storability of the flour products.
For known xylanases from different origins, xylanases from anaerobic fungi, also called rumen fungi, are gaining more attention in that anaerobic fungi usually live in the highly competitive environment of the rumen (such as the digestive tracts of ruminants and monogastric herbivores); therefore, these microorganisms evolve to yield enzymes with high activity (see Trinci et al. 1994. Anaerobic fungi in herbivorous animals. Mycol. Res. 98:129-152., which is incorporated hereinto by reference).
In view of extensive utilization, xylanases of anaerobic fungi are in great demand in various fields; however, due to the limitations of culture techniques of anaerobic fungi and slow growth rate of fungi, mass production through a natural cultivation method cannot be achieved, and thus, the use of xylanases from anaerobic fungi is hindered. Therefore, the above problem may be solved if a gene cloning method and an easily operable host cell can be utilized to express xylanases from anaerobic fungi.
Some yeasts have advantages, such as a rapid cell growth rate, suitability for high cell density cultivations, utilization of methanol as a carbon source, etc, and thus, it has been suggested in the literature that the production of recombinant proteins in a great amount can be achieved using yeasts as host cells (see Romanos et al. 1992. Foreign Gene Expression in Yeast: A Review. Yeast 8:423-488., which is incorporated hereinto by reference). However, in the industry, xylanase production on a factory scale is needed for application in various household or industrial use; for academia, a great amount of xylanase is needed for scientific research. Therefore, the above described cloning techniques still fail to reach the demand for a large-scale production of xylanase in industry or academia. As a result, a method for the mass production of a desired xylanase by enhancing the expression efficiency of host cells is in great demand.
The present invention is in response to those demands, utilizing molecular biology techniques of gene cloning to produce xylanases with high activity and thermo-tolerance. The inventors of the present application found that the level of xylanase expression can be considerably increased through the modification of a specific gene of xylanase.